Halimah wanted to show she's more than Nick's older sister, telling the cameras, "Growing up, we were always together.
"He was also singing and dancing, but he had a natural gift for tennis. I look to him a lot for inspiration. He’s such a fighter, everyone knows that. He battles for everything. Even though he’s much younger than me... If he can do it, why can’t I? What’s stopping me?
"I'm not very... out there like he is. Having Nick in the limelight has been a good and bad thing. There is added pressure. I really just want to focus on people knowing me as Halimah, not Nick’s sister. That would be amazing to achieve."
When the 31-year-old performed the track, all of the judges turned around, stunned by what they had heard.
Keith Urban, Rita Ora, Jessica Mauboy and Guy Sebastian then found out she is Nick's sister and the tennis star is apparently not that bad of a singer and dancer himself, according to Halimah.
Right after the performance, Nick appeared via Zoom with their parents.
"I just flew back from Sydney so I missed it," he told host Sonia Kruger and the judges.
"She was amazing," Sonia responded.
"She always is," Nick said.
"It was even better than your shot through the legs, Nick," Guy teased the tennis star.
While she had all four judges to pick from, Halimah chose Rita Ora, saying she's a fan of hers.
"I did not expect her to pick me, I’m really flattered. That’s an Australian song, a classic and I’m glad she trusts me. There’s a lot we can do together," Rita later told the cameras.
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